Articles of Footwear

ABSTRACT

A sole assembly for an article of footwear includes an outsole, a midsole disposed on the outsole and having a heel portion that defines a void, and first and second inserts disposed in the void. The first insert is attached to the outsole, and the second insert is disposed on top of the first insert in a manner such that the first and second inserts are movable relative to one another.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser. No. 61/513,817, filed on Aug. 1, 2011, which is incorporated by reference herein.

TECHNICAL FIELD

This disclosure relates to articles of footwear.

BACKGROUND

In general, shoes, a type of footwear, include an upper portion and a sole. When the upper portion is secured to the sole, the upper portion and the sole together define a void that is configured to securely and comfortably hold a wearer's foot. Often, the upper portion and/or sole are/is formed from multiple layers that can be stitched or adhesively bonded together. For example, the upper portion can be made of a combination of leather and fabric, or foam and fabric, and the sole can be formed from at least one layer of natural rubber. Often materials are chosen for functional reasons, e.g., water-resistance, durability, abrasion-resistance, and breathability, while shape, texture, and color are used to promote the aesthetic qualities of the shoe.

SUMMARY

In one aspect of the invention, an article of footwear includes a footwear upper and a sole assembly secured to the footwear upper. The sole assembly includes an outsole, a midsole disposed on the outsole and having a heel portion that defines a void, and first and second inserts disposed in the void. The first insert is attached to the outsole, and the second insert is disposed on top of the first insert in a manner such that the first and second inserts are movable relative to one another.

In another aspect of the invention, a sole assembly for an article of footwear includes an outsole, a midsole disposed on the outsole and having a heel portion that defines a void, and first and second inserts disposed in the void. The first insert is attached to the outsole, and the second insert is disposed on top of the first insert in a manner such that the first and second inserts are movable relative to one another.

Implementations can include one or more of the following features.

In some implementations, a portion of the second insert extends above (e.g., 1.0 mm to 3.0 mm above) top surfaces of the midsole that are adjacent to the void.

In certain implementations, the second insert is more compliant than the first insert.

In some implementations, the first insert is formed of a material having a durometer of 50 Asker C to 55 Asker C, and the second insert is formed of a material having a durometer of 40 Asker C to 45 Asker C.

In certain implementations, the first and second inserts are more compliant than the midsole.

In some implementations, the midsole includes at least one of a polyurethane and ethylene vinyl acetate.

In certain implementations, the first insert is formed of ethylene vinyl acetate having a durometer of 50 Asker C to 55 Asker C, the second insert is formed of ethylene vinyl acetate having a durometer of 40 Asker C to 45 Asker C, and the midsole is formed of ethylene vinyl acetate having a durometer of 50 Asker C to 55 Asker C.

In some implementations, the first insert is thermally bonded to the outsole.

In certain implementations, the void is sized to accommodate a heel of a wearer of the article of footwear.

In some implementations, the outsole defines a siped bottom surface.

In certain implementations, the outsole includes at least one of isobutylene rubber, butadiene rubber, styrene butadiene rubber and natural rubber.

In some implementations, the first and second inserts are formed of one or more high rebound materials (e.g., one or more materials having a resilience of 45-60 percent, as determined by the ASTM D2632 resilience test).

In certain implementations, the article of footwear further includes a footbed having a base that defines a cavity in a heel region of the footbed and an insert disposed in the cavity. The insert is formed of a material having a durometer of 30 Asker C to 35 Asker C (e.g., 33 Asker C).

In some implementations, the cavity is configured to receive a heel bone of a wearer of the article of footwear.

In certain implementations, the base is formed of a material having a durometer of 35 Asker C to 40 Asker C.

In some implementations, the base is formed of ethylene vinyl acetate.

In certain implementations, the insert is formed of thermoplastic elastomer.

In some implementations, the insert has a thickness of 2 mm to 10 mm (e.g., 4 mm).

Other aspects, features, and advantages will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a boat shoe.

FIG. 2 is an outside view of a sole assembly of the boat shoe of FIG. 1.

FIG. 3 is a bottom view of the sole assembly of the boat shoe of FIG. 1.

FIG. 4 is an inside view of the sole assembly of the boat shoe of FIG. 1.

FIG. 5 is a cross-sectional view of the sole assembly of the boat shoe of FIG. 1, taken along line A-A′ in FIG. 3.

FIG. 6 is a top view of the sole assembly of the boat shoe of FIG. 1.

FIG. 7 is a cross-sectional view of the sole assembly of the boat shoe of FIG. 1, taken along line B-B′ in FIG. 3.

FIG. 8 is a cross-sectional view of the sole assembly of the boat shoe of FIG. 1, taken along line C-C′ in FIG. 3.

FIG. 9 is a cross-sectional view of the sole assembly of the boat shoe of FIG. 1, taken along line D-D′ in FIG. 3.

FIG. 10 is a cross-sectional view of the sole assembly of the boat shoe of FIG. 1, taken along line E-E′ in FIG. 3.

FIG. 11 is a back view of the sole assembly of the boat shoe of FIG. 1.

FIG. 12 is a perspective view of a testing apparatus for a sole assembly.

FIG. 13 is a top perspective view of a sole assembly with a testing block placed on the heel portion thereof.

DETAILED DESCRIPTION

Shock and vibrations experienced while boating, in particular power boating, can cause fatigue and even muscle soreness. A person can experience forces, translated from a power boat deck, several times that of running. A reduction in the shock and vibrations experienced while boating typically enhances the boating experience. The present disclosure describes a sole assembly, and, in some examples, a shoe that reduces the shock and vibrations experienced while boating, thereby likely reducing fatigue and enhancing enjoyment of boating. The sole assemblies and shoes described herein have been found to reduce shock and vibrations more effectively than various running shoes, which many people have chosen to wear in the past while boating.

Referring to FIG. 1, a shoe 100 includes a shoe upper 110 and a sole assembly 200 secured to the shoe upper 110. Any of various different techniques, including adhesive bonding, thermal bonding, and stitching, can be used to secure the shoe upper 110 to the sole assembly 220. The sole assembly 200, as described below, is constructed in a way to reduce shock and vibrations that are transmitted to a heel bone of the wearer (e.g., by a power boat deck) during use.

As shown in FIGS. 2-6, the sole assembly 200 has a heel portion 202 and a forefoot portion 204, and includes an outsole 210 that is attached (e.g., adhesively bonded, thermally bonded, and stitched) to a midsole 220. The outsole 210 has a heel portion and a forefoot portion corresponding to the heel portion 202 and the forefoot portion 204 of the sole assembly 200.

As shown in FIGS. 5, 9, and 10, the midsole 220 forms a void or cavity 120 in which top and bottom shock absorption inserts 122, 124 are positioned. The void 120 is sized to approximately match the expected sized of a wearer's heel bone. The shock absorption inserts 122, 124 are sized and shaped to closely correspond to the size and shape of the void 120 such that the inserts 122, 124 experience little movement within the void 120 during use. The shock absorption inserts 122, 124 absorb shock and vibrations and thus reduce the stress experienced by the heel of the wearer as a result of forces applied to the sole assembly 200 (e.g., by a power boat deck). The bottom shock absorption insert 124 is attached (e.g., adhesively bonded, thermally bonded, or stitched) to the heel region of the outsole 210. The top shock absorption insert 122 is positioned atop the bottom shock absorption insert 124 but is not attached to the bottom shock absorption insert 124. Thus, the top shock absorption insert 122 is free to move relative to the bottom shock absorption insert 124 to some extent.

When shock and vibrations are applied to the heel portion 202 of the sole assembly 200, those forces and vibrations are in large part absorbed by the shock absorption inserts 122, 124. As a result, ground contact forces directly below the heel are substantially mitigated prior to be transmitted to the heel of the wearer. In this way, the shock absorption inserts 122, 124 reduce a wearer's exposure to shock and vibrations from a moving surface, such as the deck of a boat. Without wishing to be bound by theory, it is believed that the material selection of the shock absorption inserts 122, 124 and the ability of the shock absorption inserts 122, 124 to move slightly relative to one another enhances the ability of the heel portion 202 of the sole assembly 200 to mitigate forces and vibrations transmitted to the heel of the wearer during use.

Still referring to FIGS. 5, 9, and 10, the top shock absorption insert 122 is typically formed of ethylene vinyl acetate (EVA) having a durometer of 40 Asker C to 45 Asker C, and the bottom cushioning insert 124 is typically formed of EVA having a durometer of 50 Asker C to 55 Asker C. The midsole 220 is typically formed of EVA having a durometer of 50 Asker C to 55 Asker C.

The void 120 formed in the midsole 220, as noted above, is sized and shaped to accommodate a wearer's heel. In an average size adult shoe (e.g., a size 9D shoe), the void 120 has a width of about 40 mm to about 50 mm (e.g., about 45 mm) and a length of about 60 mm to about 70 mm (e.g., about 65 mm). The top and bottom shock absorption inserts 122, 124 are substantially the same size as the void 120 such that the shock absorption inserts 122, 124 can be securely positioned within the void 120 with limited front-to-back and side-to-side movement relative to the midsole 220.

The depth of the void and the thicknesses of the shock absorption inserts 122, 124 are dependent on the thickness of the sole assembly to be used for a particular style of shoe. In many implementations, the void 120 has a depth of about 8 mm to about 20 mm (e.g., about 15 mm to about 20 mm), the top shock absorption insert 122 has a thickness of about 2 mm to about 8 mm (e.g., about 4 mm to about 6 mm), and the bottom shock absorption insert 124 has a thickness of about 8 mm to about 16 mm (e.g., about 11 mm to about 13 mm).

As shown in FIGS. 5, 9, and 10, the top shock absorption insert 122 extends slightly above the void 120 (i.e., slightly above the top surfaces of the midsole 220 that are adjacent to the void 120). The top shock absorption insert 122 can, for example, extend about 1.0 mm to about 3.0 mm (e.g., about 2.0 mm) above the top surfaces of the midsole 220 adjacent to the void 120. The material of the top shock absorption insert 122 tends to compress and lose some of its height or thickness over time. Extending a portion of the top shock absorption insert 122 above the void 120 in the manner described helps to ensure that the top surface of the top shock absorption insert 122 remains at or above the level of the top surface of the midsole 220 over the course of the life of the shoe 100, and thereby helps to ensure that the shock absorption and comfort levels provided by the sole assembly 200 are maintained over the course of the life of the shoe 100.

The outsole 210 is formed of a material that provides further dampening and shock absorption. The outsole 210 is typically formed of thermoset elastomeric material, such as natural rubber. In some implementations, the outsole 210 is formed of a rubber compound including isobutylene rubber, butadiene rubber, styrene butadiene rubber and/or natural rubber, which exhibits a balance of traction and shock absorbing characteristics. The outsole 210 can have a durometer of 40 Shore A to 70 Shore A (e.g., 50 Shore A). The outsole 210, as shown in FIG. 3, has a bottom surface that has siped or molded-siped regions 218. The siped or molded-siped bottom surface provides traction on wet surfaces, such as boat decks.

In some implementations, the shoe 100 includes a removable footbed (not shown). The footbed includes a base that is formed of EVA having a durometer of 35 Asker C to 40 Asker C and defines a cavity in its heel region. The cavity of the footbed, like the cavity 120 of the midsole 220 on which the footbed sits, is typically sized and shaped to accommodate or receive a wearer's heel bone. The insert is typically formed of thermoplastic elastomer (TPE) having a durometer of 30 Asker C to 35 Asker C (e.g., 33 Asker C) and a thickness of 2 mm to 10 mm (e.g., about 4 mm). It has been found that using a footbed of this type in combination with the sole assembly 200 enhances the shock absorbing capabilities of the shoe 100.

While standing on a moving surface (e.g. boat deck), a person's ability to press his/her toes downwardly against the surface affects that person's stability on the moving surface. In some implementations, the shoe 100 includes a toe box portion configured to allow a user to easily press one or more of his/her toes downwardly against a supporting surface. The shoe 100 defines a toe spring of 1 mm to 20 mm (e.g., 15 mm) to bring the toes of a user within close proximity of the supporting surface and prevent forward rocking exhibited by shoes with greater toe springs (e.g. as with typical running shoes). As a result, this toe spring is not a mere cosmetic design choice, but instead, is chosen to provide a specific level of shoe stability suitable for standing on moving surfaces, such as the deck of a boat. Generally, shoe designers select a toe spring that is considered aesthetically pleasing. However, this larger toe spring lends the shoe to forward rocking and increases the distance user must flex his/her toes downwardly to increase stability. An upper portion of the toe box portion is constructed of one or more flexible materials to allow easy flexion of the toe box portion upwardly and downwardly. Again, a user's ability to easily flex his/her toes downwardly increases stability and prevents rocking.

The shock and vibration absorption properties of individual materials and/or constructed shoes may be measured using the following testing procedure. Referring to FIGS. 12 and 13, a shaker table 600 is equipped with a base fixture plate 610 having, for example, a diameter of about 30 inches (762 mm) and a thickness of about 2 inches (51 mm) (e.g., made of 50-52 Aluminum). A cross bar 620 (e.g., having length of about 348 mm, a width of about 39 mm, and a thickness of about 19.5 mm) defines first and second apertures 622, 624 for receiving respective first and second cross bar rods 626, 628 (e.g., ⅜ inch (9.5 mm) diameter, 16 course thread) to attach the cross bar 620 to the base fixture plate 610. The sole assembly 200 is placed on the base fixture plate 610. The sole assembly samples to be tested should be conditioned to the temperature and humidity of the testing facility by bringing them to the testing facility at least 24 hours prior to testing.

In the example shown, right and left sole assemblies 200 are placed on the base fixture plate 610. A heel block 630 (e.g., an aluminum block having a length of about 38 mm, a width of about 38 mm, and a thickness of about 26 mm high) is used to simulate the heel bone and is placed substantially centered on the heel portion 202 of each sole assembly 200 with a rearward edge located a distance D of about 15% an overall length L of the sole assembly 200. A weight 640 (e.g., steel bar having length of 465 mm, width of 100 mm, and height of 50.5 mm and weighing 42 lbs (19 kg)) is placed over the heel block 630 in the heel portion 202 of each sole assembly 200. The cross bar 620 secures the weight 640 in place. Nuts 627, 629 are tightened on the respective threaded cross bar rods 626, 628 to 1 in-lb for shock testing and 10 in-lb for vibration testing. A rubber pad 642 having a thickness of about ¼ inch (6.35 mm), a durometer of between about 50 Shore A and about 55 Shore A, a length of 100 mm, and a width of about 39 mm is inserted between cross bar 620 and the weight 640 to deaden any ringing generated there between. A monitor accelerometer 650 is disposed on the weight 640 (e.g., about 1 inch (25.4 mm)) from the cross bar 620, which is centered width-wise on the weight 640. The monitor accelerometer 650 measure shock and vibrations that a supposed user of the sole assembly 200 would experience. A control accelerometer 660 is disposed on the base fixture plate 610 for measuring the actual input shocks and vibrations (in g's) delivered by the shaker table 600.

A minimum of 5 test repetitions at least 2 hours apart and on at least 2 different days should be executed to acquire data. In addition, “control samples” should be the first and last samples tested each day. Control samples are a predetermined group of items, generally selected towards the beginning of the project (3-5 samples is reasonable). Often, these “controls” are the project benchmarks, most relevant items, or the best performing sample(s) (can be shoes, materials, or assembled parts). Check that “control” results are similar through the course of day and from one day to the next.

Shock testing includes performing sine shock pulses on the shaker table 600 as follows (all with 10 ms durations): 1 g pulse, then re-torque the nuts 627, 629; 3 g pulse, then re-torque the nuts 627, 629; and 5 g pulse, then re-torque the nuts 627, 629. Vibration testing includes performing a half-sine sweep 5-200 Hz at 0.5 g's at 1 octave per minute on the shaker table 600. Signals of the monitor accelerometer 650 and the control accelerometer 660 are recorded during execution of the testing.

Table 1 below provides summary of shock testing results across a number of shoes, including the shoe 100 (referred to as “ASV Production” in the table) and a number of shoes without the shock absorbing inserts described herein. While shock testing with a sine shock pulse at 1 g, the shoe 100 (ASV) provided a 27% reduction in the shock wave transmitted to a user's heel relative to wearing no shoe, while shoes without the shock absorbing inserts described herein provided between an 21% reduction and a 36% amplification of the shock wave. While shock testing with a sine shock pulse at 3 g's, the shoe 100 (ASV) provided a 41% reduction in the shock wave transmitted to a user's heel relative to wearing no shoe, while shoes without the shock absorbing inserts described herein provided between a 38% reduction and a 21% amplification of the shock wave. While shock testing with a sine shock pulse at 5 g's, the shoe 100 (ASV) provided a 45% reduction in the shock wave transmitted to a user's heel relative to wearing no shoe, while shoes without the shock absorbing inserts described herein provided between a 41% reduction and a 26% amplification of the shock wave.

% % % Change Change Change over over over Shoe Δ 1 g input Δ 3 g input Δ 5 g input ASV Production −0.34 −27% −1.21 −41% −2.33 −45% Sperry Cabo −0.27 −21% −1.10 −38% −2.15 −41% Rockport XCS Nausori −0.24 −18% −0.98 −34% −2.05 −40% Sperry SB1070 −0.22 −18% −1.10 −39% −2.27 −45% Rugged Shark Bill −0.23 −18% −0.93 −32% −1.90 −37% Dance Merrell Waterpro −0.2 −16% −1.01 −35% −2.04 −39% Columbia Marine Tech −0.17 −14% −1.03 −36% −2.33 −45% Nike Shox −0.17 −13% −1.01 −35% −2.06 −40% Sperry Largo −0.16 −12% −0.80 −27% −1.79 −35% NB Zip (Grey) −0.15 −12% −0.95 −33% −2.02 −39% Sperry Cabo Thong −0.15 −12% −0.69 −24% −1.26 −25% NB Athletic −0.15 −12% −0.82 −28% −1.86 −36% Adidas Microbounce −0.14 −11% −0.95 −33% −1.95 −38% Sperry Gold Driver −0.14 −11% −0.63 −22% −1.26 −24% Puma Jago −0.11 −8% −0.85 −29% −1.51 −30% Sperry Billfish −0.11 −8% −0.82 −28% −1.71 −33% Rugged Shark Aquaire −0.09 −7% −0.64 −22% −1.16 −23% Pro Cole Haan Aire −0.09 −7% −0.61 −21% −0.8 −15% Everett Clarks Zarkon −0.09 −7% −0.76 −26% −1.54 −30% Sperry Figawi II −0.09 −7% −0.95 −33% −1.97 −39% Crocs −0.07 −5% −0.87 −30% −1.89 −37% Mizuno Wave −0.05 −4% −0.86 −30% −1.94 −37% West Marine −0.06 −4% −0.60 −21% −1.47 −28% Performance Moc Puma Decker −0.03 −3% −0.69 −24% −1.43 −28% Nike Air −0.03 −3% −0.84 −29% −1.71 −33% Sperry Gold Cup −0.02 −2% −0.56 −19% −1.40 −28% Salomon Tech −0.02 −2% −0.79 −27% −1.97 −38% Amphibian Helly Hansen Hydrator 0.008 1% −0.34 −12% −0.56 −11% Salomon Karma 0.02 2% −0.56 −19% −1.31 −26% CMEVA Adidas 0.028 2% −0.46 −16% −1.14 −22% Sebago Clovehitch 0.032 2% −0.66 −23% −1.72 −34% Sperry Newport 0.04 3% −0.48 −17% −1.11 −22% Sperry Santa Cruz 0.06 5% −0.62 −22% −1.47 −29% Thong Sperry Mako 0.143 11% −0.31 −11% −0.53 −10% Sperry Tremont 0.225 17% −0.06 −2% −0.09 −2% Sperry A/O 0.37 29% 0.01 0% −0.07 −1% Sebago Spinnaker 0.464 36% 0.61 21% 1.31 26%

Across all of the shoes tested the ASV shoe provided the greatest reduction in shock transmission to a user.

While certain implementations have been described, other implementations are possible.

While the shock absorption inserts 122, 124 have been described as being formed of EVA, other materials can alternatively or additionally be used to effectively dampen shock and vibrations acting on the heel region 202 of the shoe 100. Examples of other materials from which the shock absorption inserts 122, 124 can be formed include polyurethane foam and TPE foam.

It has been found that certain combinations of shock absorption insert materials are particularly effective at absorbing shock and vibrations acting on the heel portion 202 of the sole assembly 200 of the shoe 100. For example, using high rebound materials for the top and bottom inserts 122, 124 can provide desirable results. High rebound materials are materials having a resilience of 45-60 percent, as determined by the ASTM D2632 resilience test. In some implementations, the top shock absorption insert 122 is formed of TPE having a durometer of 30 Asker C to 35 Asker C (e.g., 33 Asker C) and the bottom shock absorption insert 124 is formed of EVA having a durometer of 50 Asker C to 55 Asker C.

It is believed that using high rebound materials to form the top insert 122 and high shock absorbing materials (e.g., materials having a resilience of 20 percent or less, as determined by the ASTM D2632 resilience test) to form the bottom insert 124 can also provide suitable shock and vibration absorption. In certain implementations, for example, the top shock absorption insert 122 is formed of EVA having a durometer of 40 Asker C to 45 Asker C and the bottom shock absorption insert 124 is formed of polyurethane foam having a durometer of 50 Asker C to 55 Asker C.

While the midsole 220 has been described as being formed of EVA in certain implementations discussed above, the midsole 220 can alternatively or additionally be constructed of one or more other shock absorbing materials, such as shock absorbing polyurethane. In some implementations, the midsole 220 has a durometer of 40 Asker C to 70 Asker C (e.g., 50 Asker C).

While the midsole 220 has been illustrated as directly contacting and resting on the outsole 210 in the forefoot portion of the sole assembly 200, in some implementations, the forefoot portion of the sole assembly 200 includes a forefoot cushion layer disposed between the outsole 210 and the midsole 220. The cushion layer can, for example, be disposed in a recess defined in a forefoot region of the midsole 220. The forefoot cushion layer provides additional shock absorption and cushioning for a user's foot. The forefoot cushion layer can be made of polyurethane (e.g. polyurethane foam) and can have a durometer of 40 Asker C to 70 Asker C (e.g., 50 Asker C).

While the sole assembly 200 has been described as including two inserts 122, 124 within the cavity 120 defined by the midsole 220, more than two inserts (e.g., three, four, five, or six inserts) can alternatively be used.

While the footbed has been described as being removable, in certain cases, the footbed may be permanently affixed within the shoe.

While the insert for the footbed has been described as being formed of TPE, in certain implementations, the footbed insert can be formed of other high rebound materials, such as EVA having a durometer of 40 Asker C to 45 Asker C.

Although the sole assembly 200 has been shown as being attached to a shoe, it may be used for other types of articles of footwear, including, but not limited to boots, sandals, flip-flops, etc.

While the footwear have been described as reduce shock and vibrations that are transmitted to the heel of the wearer from the deck of a boat, it should be understood that the footwear described herein can be used to reduce such shock and vibrations from a variety of other moving surfaces, such as construction vehicles, large machinery, etc.

Other implementations are within the scope of the following claims. 

1. An article of footwear comprising: a footwear upper; and a sole assembly secured to the footwear upper, the sole assembly comprising an outsole; a midsole disposed on the outsole, a heel portion of the midsole defining a void; and first and second inserts disposed in the void, the first insert being attached to the outsole, and the second insert being disposed on top of the first insert in a manner such that the first and second inserts are movable relative to one another.
 2. The article of footwear of claim 1, wherein a portion of the second insert extends above top surfaces of the midsole that are adjacent to the void.
 3. The article of footwear of claim 2, wherein the portion of the second insert extends about 1.0 mm to about 3.0 mm above the top surfaces of the midsole that are adjacent to the void.
 4. The article of footwear of claim 1, wherein the second insert is more compliant than the first insert.
 5. The article of footwear of claim 4, wherein the first insert is formed of a material having a durometer of 50 Asker C to 55 Asker C, and the second insert is formed of a material having a durometer of 40 Asker C to 45 Asker C.
 6. The article of footwear of claim 1, wherein the first and second inserts are more compliant than the midsole.
 7. The article of footwear of claim 1, wherein the midsole comprises at least one of a polyurethane and ethylene vinyl acetate.
 8. The article of footwear of claim 1, wherein the first insert is formed of ethylene vinyl acetate having a durometer of 50 Asker C to 55 Asker C, the second insert is formed of ethylene vinyl acetate having a durometer of 40 Asker C to 45 Asker C, and the midsole is formed of ethylene vinyl acetate having a durometer of 50 Asker C to 55 Asker C.
 9. The article of footwear of claim 1, wherein the first insert is thermally bonded to the outsole.
 10. The article of footwear of claim 1, wherein the void is sized to accommodate a heel of a wearer of the article of footwear.
 11. The article of footwear of claim 1, wherein the outsole defines a siped bottom surface.
 12. The article of footwear of claim 11, wherein the outsole comprises at least one of isobutylene rubber, butadiene rubber, styrene butadiene rubber and natural rubber.
 13. The article of footwear of claim 1, wherein the first and second inserts are formed of one or more high rebound materials.
 14. The article of footwear of claim 13, wherein the first and second inserts are formed of one or more materials having a resilience of 45-60 percent, as determined by the ASTM D2632 resilience test.
 15. The article of footwear of claim 1, further comprising one or more additional inserts disposed on the second insert.
 16. The article of footwear of claim 1, further comprising a footbed having a base that defines a cavity in a heel region of the footbed and an insert disposed in the cavity, the insert being formed of a material having a durometer of 30 Asker C to 35 Asker C.
 17. The article of footwear of claim 16, wherein the cavity is configured to receive a heel bone of a wearer of the article of footwear.
 18. The article of footwear of claim 16, wherein the base is formed of a material having a durometer of 35 Asker C to 40 Asker C.
 19. The article of footwear of claim 18, wherein the base is formed of ethylene vinyl acetate.
 20. The article of footwear of claim 19, wherein the insert is formed of thermoplastic elastomer.
 21. The article of footwear of claim 19, wherein the insert has a thickness of 2 mm to 10 mm.
 22. A sole assembly for an article of footwear, the sole assembly comprising: an outsole; a midsole disposed on the outsole, a heel portion of the midsole defining a void; and first and second inserts disposed in the void, the first insert being attached to the outsole, and the second insert being disposed on top of the first insert in a manner such that the first and second inserts are movable relative to one another. 